const MyQueue=function(){
    // 初始化两个栈
    this.stack1=[];
    this.stack2=[];
}
// 双端队列
MyQueue.prototype.push=function(x){
    this.stack1.push(x);
}

MyQueue.prototype.pop=function(){
    if(this.stack2.length<=0){
        while(this.stack1.length!==0){
            this.stack2.push(this.stack1.pop());
        }
    }
    this.stack2.pop()
}

MyQueue.prototype.peek=function(){
    if(this.stack2.length<=0){
        while(this.stack1.length!=0){
            this.stack2.push(this.stack1.pop());
        }
    }
    const stack2Len=this.stack2.length;
    return stack2Len && this.stack2[this.stack2-1];
}

MyQueue.prototype.empty=function(){
    return !this.stack1.length && !this.stack2.length;
}